Speakers have recently been compacted, and input power to the speaker is increasing.
There are two methods for connecting a coil wire of a voice coil to an external input terminal of speaker, as is disclosed in Japanese Patent Laid-Open No. H6-209497. In one method, the coil wire is directly connected to the external terminal, which is herein called type A. In another method, the coil wire is connected to the external terminal by means of a flexible wire (FW), which is herein called type B. The flexible wire (FW) is preferred to be a wire in which a core thread is wound by a copper foil, and then the copper foiled core threads are braided together or stranded, forming the FW which is generally called a “kinshisen” in Japanese.
FIG. 4 is a cross-sectional view of a conventional external-magnet type speaker. Magnetic circuit 40 is composed of lower plate 10 including a center pole, upper plate 30, and magnet 20. Frame 50 is mounted on an upper side of the magnetic circuit 40. An outer rim of diaphragm 60 is fixed to an inner rim of frame 50, and an inner rim of diaphragm 60 is fixed to an outer rim of voice coil bobbin 80 placed in magnetic gap 40A of magnetic circuit 40. Voice coil bobbin 80 is wound up by voice coil 70. External input terminal 90 is attached to frame 50. Damper 100 is fixed to frame 50 and voice coil bobbin 80. Dust cap 110 is fixed over and above a joint portion of diaphragm 60 and voice coil bobbin 80. The speaker described above belongs to type B in the connecting method. Coil wire 12 is wound on voice coil bobbin 80, and each end of the wire is drawn from voice coil bobbin 80 along an axis of the bobbin and is connected to one end of FW 13 at an upper surface of diaphragm 60, while the other end of the FW is connected to external input terminal 90. Another example of type B is shown in FIG. 5, in which each end of coil wire 12 is drawn along the axis of voice coil bobbin 80 and is connected to one end of FW 13 at an outer peripheral surface of voice coil bobbin 80, the other end of the FW being connected to external input terminal 90.
In type A, although it is not illustrated, each end of coil wire 12 is drawn from the outer periphery of voice coil bobbin 80 and is directly connected to external input terminal 90.
Type B speaker which is shown in FIGS. 4 and 5, in which coil wire 12 is relayed by FW 13 to be connected to external input terminal 90, withstands a large amplitude motion caused by a large input signal. However, on the other hand, FW 13 is thick and heavy. Furthermore, because voice coil wire 12 is connected to FW 13 at the upper surface of diaphragm 60 or at the outer peripheral surface of voice coil bobbin 80, weight of adhesive and solder is applied to voice coil bobbin 80 and diaphragm 60, biasing their weight toward an outer region and thus obstructing smooth amplitude motion and causing unsatisfactory sound quality. When the bias is serious, it becomes a reason for sound failure. Type A, in which coil wire 12 is directly connected to external input terminal 90, achieves smoother amplitude motion of voice coil bobbin 80 and diaphragm 60 by an amount of the FW being saved. However, because coil wire 12 has two bending points, one where the wire is drawn out of voice coil bobbin 80 and another where the wire is connected to external terminal 90, the probability of wire breakage tends to increase as power at an input signal increases accompanying a larger amplitude motion.
It is an object of the present invention to provide a speaker in which the coil wire withstands the large amplitude motion which the voice coil bobbin and the diaphragm experience when vibrating, and in which the biased weight of the voice coil bobbin and the diaphragm caused by the constitution of the coil wire is controlled to be a minimum. Thus, the speaker is endowed with a high reliability and a superior sound quality.